U.S. patent application number 15/062997 was filed with the patent office on 2016-09-15 for optical module having optical unit enclosing semiconductor optical device leveled to surface fixing optical unit.
The applicant listed for this patent is Sumitomo Electric Device Innovations, Inc.. Invention is credited to Takeshi Okada.
Application Number | 20160266318 15/062997 |
Document ID | / |
Family ID | 56886607 |
Filed Date | 2016-09-15 |
United States Patent
Application |
20160266318 |
Kind Code |
A1 |
Okada; Takeshi |
September 15, 2016 |
OPTICAL MODULE HAVING OPTICAL UNIT ENCLOSING SEMICONDUCTOR OPTICAL
DEVICE LEVELED TO SURFACE FIXING OPTICAL UNIT
Abstract
A bi-directional optical module that provides an Rx unit and a
Tx unit, where optical axes are perpendicular to each other, is
disclosed. The optical module provides a housing that installs a
WDM filter therein and assembles the coupling unit in a surface
through the front alignment unit, the Tx unit in another surface
opposite to the former surface, and the Rx unit in still another
surface connecting the former two surfaces through the rear
alignment unit. The axes of the Tx unit and the coupling unit are
in parallel to each other, but the axis of the Rx unit is in
perpendicular to the former two axes. The Rx unit installs a
photodiode (PD) with an optically sensitive surface leveled with
the surface of the rear alignment unit to which the Rx unit is
attached.
Inventors: |
Okada; Takeshi;
(Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Electric Device Innovations, Inc. |
Yokohama-shi |
|
JP |
|
|
Family ID: |
56886607 |
Appl. No.: |
15/062997 |
Filed: |
March 7, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4246 20130101;
G02B 6/4215 20130101; G02B 6/4237 20130101; G02B 6/4244
20130101 |
International
Class: |
G02B 6/293 20060101
G02B006/293; G02B 6/42 20060101 G02B006/42 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2015 |
JP |
2015-045893 |
Claims
1. An optical module, comprising: an optical unit enclosing a
semiconductor optical device having an optically sensitive surface,
the semiconductor optical device converting one of an optical
signal and an electrical signal into another of the optical signal
and the electrical signal; and a primary assembly having an end
surface that fixes the optical unit thereto, wherein the optically
sensitive surface of the semiconductor optical device is aligned in
a level thereof with the end surface of the primary assembly.
2. The optical module of claim 1, wherein the optical unit is a
receiver optical unit that encloses a semiconductor photodiode (PD)
having the optically sensitive surface for receiving an optical
signal entering the optical module from an external.
3. The optical module of claim 1, wherein the optical unit is a
transmitter optical unit that encloses a semiconductor laser diode
(LD) having the optically sensitive surface from which an optical
signal is emitted to an external of the optical module.
4. The optical module of claim 1, wherein the optical unit is fixed
to the primary assembly by fillet welding.
5. The optical module of claim 1, further including a coupling unit
having an optical axis and being fixed to the primary assembly,
wherein the optical axis of the coupling unit makes a right angle
with respect to an optical axis of the optical unit.
6. The optical module of claim 5, wherein the end surface of the
primary assembly extends in parallel to the optical axis of the
coupling unit.
7. The optical module of claim 5, wherein the primary assembly
includes a rear alignment unit that includes a rear lens holder and
a rear joint sleeve, the rear lens holder having a cylindrical
shape with a bore that secures a rear lens therein, the rear joint
sleeve having a cylindrical shape with a bore that receives the
rear lens holder therein, and wherein the rear joint sleeve has the
end surface of the primary assembly to which the optical unit is
fixed.
8. The optical module of claim 7, wherein the rear joint sleeve is
fixed to the rear lens holder by piercing welding.
9. The optical module of claim 7, wherein the optical unit provides
a cap that encloses the semiconductor optical device therein, the
cap having a flange that is welded to the end surface of the rear
joint sleeve.
10. The optical module of claim 7, wherein the primary assembly
further includes a filter holder that secures a wavelength division
multiplexing (WDM) filter therein, the WDM filter having a normal
line making a half right angle with respect to the optical axis of
the coupling unit and the optical axis of the optical unit.
11. The optical module of claim 10, wherein the filter holder has a
mounting surface, a Tx bore, and an Rx bore, the Tx bore having an
axis extending in parallel to the optical axis of the coupling
unit, the Rx bore having an axis extending in parallel to the
optical axis of the optical unit, the Tx bore and the Rx bore each
exposing on the mounting slope, the mounting slope mounting the WDM
filter such that the axis of the Tx bore intersects the axis of the
Rx bore at a surface of the WDM filter, and wherein the rear lens
holder is fixed to the filter holder.
12. The optical module of claim 5, wherein the housing further
includes a filter holder that secures a wavelength division
multiplexing (WDM) filter therein, the WDM filter having a normal
line making a half right angle with respect to the optical axis of
the coupling unit and the optical axis of the optical unit.
13. The optical module of claim 12, further including a front
alignment unit that provides a front lens holder and a front joint
sleeve, the front lens holder having a cylindrical shape with a
bore that secures a front lens therein, the front joint sleeve
having an end surface and a cylindrical shape with a bore that
receives the front lens holder therein, the end surface of the
front joint sleeve fixing the coupling unit thereto.
14. The optical module of claim 12, further including another
optical unit that converts one of an optical signal and an
electrical signal into another of the optical signal and the
electrical signal, the optical unit enclosing a semiconductor
optical device having an optically sensitive surface, wherein the
another optical unit has an optical axis extending in parallel to
the optical axis of the coupling unit and in perpendicular to the
optical axis of the optical unit.
15. The optical module of claim 14, wherein the optical unit is a
receiver optical unit that encloses a semiconductor photodiode (PD)
having the optically sensitive surface for receiving an optical
signal entering the optical module from an external and reflected
by the WDM filter, and the another optical unit is a transmitter
optical unit that encloses a semiconductor laser diode (LD) having
the optically sensitive surface from which another optical signal
is emitted to an external of the optical module transmitting
through the WDM filter.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present application relates to an optical module, in
particular, the present application relates to an optical module
having an optical unit that encloses a semiconductor optical device
with a sensitive surface whose level is aligned with an end surface
of a housing to which the optical unit is fixed.
[0003] 2. Background Arts
[0004] A wavelength division multiplexing (WDM) and/or a
bi-directional communication using two wavelengths for a single
optical fiber have been become popular by utilizing the
orthogonality with respect to the wavelength. Also, the
communication speed, or the communication capacity of such a system
reaches and sometimes exceeds 10 Gbps. A light-receiving device,
typically, a semiconductor photodiode (PD) and an avalanche
photodiode (APD), is strongly requested to decrease parasitic
capacitance including junction capacitance thereof. Accordingly, an
optically sensitive area of such a PD has become narrower, where a
diameter of the optically sensitive area is, for example, 30 .mu.m
or shorter to reduce the junction capacitance. The assembly of the
optical module implementing such PD with a narrowed sensitive area
has become critical because of a limited positional tolerance in
the optical alignment thereof.
SUMMARY OF THE INVENTION
[0005] An aspect of the present application relates to an optical
module that includes an optical unit and a primary assembly. The
optical unit may be a receiver optical unit and/or transmitter
optical unit, where the optical unit encloses a semiconductor
optical device. The semiconductor optical device of the invention
converts one of an optical signal and an electrical signal into
another of the optical signal and the electrical signal, and has an
optically sensitive surface. The primary assembly has an end
surface to which the optical unit is fixed. A feature of the
optical module of the present invention is that the optically
sensitive surface of the semiconductor optical device in a level
thereof is aligned to the end surface of the primary subassembly.
In other words, the optically sensitive surface of the
semiconductor optical device is within a virtual plane extending
from the end surface of the primary assembly to which the optical
unit is fixed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The foregoing and other purposes, aspects and advantages
will be better understood from the following detailed description
of a preferred embodiment of the invention with reference to the
drawings, in which:
[0007] FIG. 1 is a perspective view showing a bi-directional
optical module according to an embodiment of the present
invention;
[0008] FIG. 2 shows a cross section of the bi-directional optical
module shown in FIG. 1;
[0009] FIG. 3 is an exploded cross section of respective parts in
the bi-directional optical module shown in FIG. 1;
[0010] FIG. 4 is a cross section showing an optical receiver unit,
a second lens holder, and a second J-sleeve assembled by welding to
each other;
[0011] FIG. 5A shows a cross section of the optical receiver unit
before being assembled with the other members, and FIG. 5B shows
another cross section of the optical receiver unit after being
assembled with the other members;
[0012] FIG. 6 explains a mechanism to align the optical receiver
module according to the present invention; and
[0013] FIGS. 7A and 7B show cross sections of a conventional
optical receiver module with mechanisms of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0014] Next, some embodiments according to the present invention
will be described as referring to drawings. In the explanation of
the drawings, numerals or symbols same with or similar to each
other will refer to elements same with or similar to each other
without duplicated explanations.
[0015] A convention optical module applicable to the high speed
optical communication will be first explained. A process to
assembly a receiver optical unit that implements a photodiode (PD)
with a restricted sensitive area requests an optical alignment and
a fixation with extremely preciseness. The YAG laser welding and/or
an adhesive resin are widely used for the permanent fixation of
optical components once optically aligned with extremely
preciseness. But, the former fixation inevitably accompanies with
misalignment at the welding and the latter fixation accompanies
with shrinkage at the solidification, both of which causes the
misalignment of the optical components.
[0016] FIGS. 7A and 7B schematically show an optical module before
and after assembling components, respectively. The optical module
100 shown in FIGS. 7A and 7B is the type of a bi-directional
optical module including a receiver optical unit 101, a transmitter
optical unit and a coupling unit, where the latter two units are
omitted in FIGS. 7A and 7B. The optical module further is fixed to
a lens holder 104 that secures a lens 104a therein, to which the
optical receiver unit 101 is fixed. The optical module 100 aligns,
along the optical axis P thereof, the optical receiver unit 101,
which is held by a holder ring 102, with the J-sleeve 103 by
sliding the holder ring within a bore of the J-sleeve 103. Then,
the J-sleeve 103 is welded to the holder ring 102. Also, the
optical receiver unit 100 is aligned in directions perpendicular to
the optical axis P by sliding the J-sleeve 103 on an end surface
104b of the lens holder 104, then fixed thereto by fillet welding.
Thus, the optical receiver unit 101 is fixed to the lens holder 104
after the precise alignment in three directions.
[0017] However, the conventional arrangements in the optical module
100 shown in FIG. 7A, the optically sensitive surface 101b of the
optical device 101a is possibly inclined with the optical axis P
after the fixation of the optical receiver unit 101 to the lens
holder 104 by the welding, even when the optical alignment
therebetween described above is once performed precisely, as shown
in FIG. 7B.
[0018] FIG. 1 is a perspective view showing a bi-directional
optical module according to an embodiment of the present invention;
FIG. 2 shows a cross section of the bi-directional optical module
shown in FIG. 1; and FIG. 3 is an exploded cross section of
respective parts in the bi-directional optical module shown in FIG.
1. The optical module shown in FIG. 1 is a type of a bi-directional
optical module capable of transmitting an optical signal (Tx
signal) with a wavelength and concurrently receiving another
optical signal (Rx signal) with another wavelength but for a single
external fiber. The optical module 1 includes a receiver optical
unit (Rx unit) 2, a transmitter optical unit (Tx unit) 3, and a
coupling unit 4 that receives an external optical connector
securing the single optical fiber. The wavelengths of the Tx signal
and the Rx signal are different from each other. The optical module
1 further provides a primary assembly 5 to which the Rx unit 2, the
Tx unit 3, and the coupling unit 4 are fixed thereto.
[0019] The Rx unit 2 implements a photodiode (PD) 2a that receives
the Rx signal, and fixed to the primary assembly 5 such that an
optical axis thereof, or the optical axis of the PD 2a, makes a
right angle against an optical axis of the coupling unit 4. The Tx
unit 3 implements a laser diode (LD) that emits the Tx signal
toward the coupling unit 4, and fixed to the primary assembly 5
such that an optical axis thereof, or the optical axis of the LD,
is in parallel to the optical axis of the coupling unit 4. In an
embodiment shown in FIG. 1, the Tx unit 3 has a box-shaped package,
which is often called as a butterfly package, but the optical
module 1 may implement the Tx unit 3 with a co-axial package same
with those of the Rx unit 2.
[0020] The primary assembly 5, as illustrated in FIG. 2, includes a
front alignment unit 6 having a front lens holder 6a that secures a
front lens 6c, and the front J-sleeve 6b; a rear alignment unit 9
including a rear lens holder 9a that secures a rear lens 9c, and a
rear J-sleeve 9b; a filter holder 8 including a wavelength division
multiplexing (WDM) filter 8a, and a housing 7. The housing 7
receives the filter holder 8 and secures the coupling unit 4 and
the Rx unit 2 through the front alignment unit 6 and the rear
alignment unit 9, respectively. In the description below, a
direction "front" or "forward" corresponds to the side where the
coupling unit 4 is provided, while, another direction "rear"
corresponds to a side where the Rx unit 2 is provided. However,
those descriptions are defined merely from an explanation sake, and
do not narrower the scope of the invention at all. The coupling
unit 4 is, as illustrated in FIG. 2, is fixed to the primary
assembly 5 through the front alignment unit 6 as optically aligning
with respect to directions in parallel and in perpendicular to the
optical axis of the coupling unit 4. Details of the coupling unit 4
and the front alignment unit 6 will be described later. The front
lens 6c collimates the Rx signal provided from the single optical
fiber through the coupling unit 4; but concentrates the Tx signal
provided from the Tx unit 3 onto an end of the coupling unit 4.
[0021] In addition to the front alignment unit 6, as illustrated in
FIGS. 1 and 3, the primary assembly 5 provides a cylindrical
housing 7, a filter holder 8 that secures a WDM filter 8a, a rear
alignment unit 9 including the rear lens holder 9a that secures a
rear lens 9c, and a arear J-sleeve 9b that connects the Rx unit 2
to the rear lens holder 9a. The Rx unit 2 is aligned with respect
to the housing 7 by a combination of the rear lens holder 9a and
the rear J-sleeve 9b, and fixed thereto. The rear lens holder 9a is
preferably a type of an aspheric lens because a spherical lens
inherently shows a substantial aberration and is unable to
concentrate an optical beam into a restricted area of a PD 2a that
often has a sensitive area smaller than 20 .mu.m in a diameter
thereof.
[0022] The optical module 1 thus described optically couples the Tx
signal emitted from the Tx unit 3 with a coupling fiber 4e secured
in the coupling unit 4 through the WDM filter 8a and the front lens
6c; while, the Rx signal provided from the coupling fiber 4e to the
Rx unit 2 through the front lens 6c, reflected by the WDM filter
8a, and concentrated by the rear lens 9c on the Rx unit 2. Because
the Rx unit 2 is fixed to a side of the housing 7, that is, the
optical axis of the coupling unit 4 is perpendicular to the optical
axis of the Rx unit 2; the Rx unit 2, exactly, the optically
sensitive surface of the PD 2a is possibly inclined with respect to
the optical axis of the coupling unit 4 after the fixation to the
housing 7. In other words, the optically sensitive surface of the
PD 2a becomes nonparallel to an end surface of the primary assembly
5 to which the Rx unit 2 is fixed.
[0023] FIG. 4 is a cross section of the Rx unit 2, the rear
J-sleeve 9b, and the rear lens holder 9a to which the Rx unit 2 is
fixed. FIG. 5A shows a cross section of the Rx unit 2 before being
fixed to the primary assembly 5 and FIG. 5B shows a cross section
of the Rx unit 2 after the fixation to the primary assembly 5.
[0024] The Rx unit 4, as illustrated in FIG. 4, includes in
addition to the PD 2a, a stem 2c through which lead pins 2b pierce.
The PD 2a is mounded on the stem 2c through a sub-mount 2d. The
lead pins 2b provide biases to the PD 2a and extract electrical
signals corresponding to the Rx signal therethrough. The cap 2e,
which has a flange 2g forms a space into which the PD 2a and the
sub-mount 2d are enclosed. The cap 2e also provides a window 2f for
sealing the space air-tightly, through which the Rx signal enters
the PD 2a. The sub-mount 2d may be made of aluminum nitride (AlN),
and the cap 2e, which may be made of alloy of nickel (Ni), cobalt
(Co), and iron (Fe), often called as Kovar.TM., provides a window
2f made of material transparent for light subject to the Rx unit
2.
[0025] The rear J-sleeve 9b, which has a cylindrical shape with a
bore 9d, receives the rear lens holder 9a from one of ends of the
boar 9d and the Rx unit 2 from the other end of the bore 9d. The
pierce welding fixes the rear lens holder 9a to the rear J-sleeve
9b; accordingly, a wall of the rear J-sleeve 9b is formed thin. The
Rx unit 2 is fixed in an end surface 9e of the rear J-sleeve 9b.
Specifically, a surface 2h of the flange 2g of the cap 2e is fixed
to the end surface 9e of the rear J-sleeve 9b by the fillet
welding.
[0026] The optical alignment between the Rx unit 2 and the primary
assembly 5 along the optical axis of the Rx unit 2 may be carried
out by procedures same with those between the primary assembly 5
and the coupling unit 4 through the front alignment unit 6. That
is, the optical alignment between the Rx unit 2 and the primary
assembly 5 along the optical axis may be carried out by adjusting
an overlapped length between the rear J-sleeve 9b and the rear lens
holder 9a; while, the optical alignment between the Rx unit 2 and
the primary assembly 5 within a plane perpendicular to the optical
axis of the Rx unit 2 may be performed by sliding the Rx unit 2 on
the end surface 9e of the rear J-sleeve 9b within a gap formed
between the outer surface of the cap 2 and the inner surface of the
bore 9d of the rear J-sleeve 9b.
[0027] A feature of the optical module 1 of the present embodiment
is that the surface 2h of the flange 2g of the cap 2e in a level
thereof is aligned with the optically sensitive surface 2i of the
PD 2a. That is, the optical sensitive surface 2i of the PD 2a and
the surface 2h facing the rear lens holder 10 are positioned within
a same plane. As a result, as shown in FIGS. 5A and 5B, even when
the fillet welding between the cap 2e and the rear lens holder 10
makes the optical axis of the Rx unit 2, namely, the optical axis
of the optically sensitive surface 2i of the PD 2a inclined with
respect to the optical axis P of the rear J-sleeve 9b, the
misalignment of the optically sensitive surface 2i of the PD 2a may
be effectively restricted, which means that even when the optically
sensitive surface 2i of the PD 2a is formed relatively narrower to
reduce the junction capacitance thereof, the optical alignment
between the PD 2a and the rear J-sleeve 9b may be realized.
[0028] FIG. 6 explains a mechanism to align the optical receiver
module according to the present invention. Assuming parameters L,
d, and D are a distance between the surface 2h of the flange 2g to
the optically sensitive surface 2i of the PD 2a, increment or
decrement of the distance above after the welding, and an outer
diameter of the flange 2g, respectively, the inclined angle .theta.
and deviations (dx, dz) are denoted by: [0029] .theta.=tan.sup.-1
(d/D), [0030] dx=D/2*(1-cos .theta.)+L*sin .theta., [0031]
dz=D/2*sin .theta.+L*(1-cos .theta.). Because the
increment/decrement d is generally far less than the outer
dimension D of the flange 2g, d<<D; we may regard as sin
.theta..about..theta. and cos .theta..about.1. Accordingly, the
deviation is given by:
[0031] (dx, dz)=(L.times..theta., D/2.times..theta.).
Thus, the physical arrangement between the optically sensitive
surface 2i of the PD 2a and the surface 2h of the flange 2g to be
welded to the rear J-sleeve 9b may effectively restrict the
positional deviation of the optically sensitive surface 2i of the
PD with respect to the rear J-sleeve 9b. In other words, the
positional relation of the optically sensitive surface 2i of the PD
2a and the surface 2h of the flange 2g is insensitive to the
misalignment due to the welding.
[0032] The arrangement of the Rx unit 2 and the rear J-sleeve may
have preferable relations of an outer diameter of the stem 2c is
smaller than that of the cap 2g, and the output diameter of the cap
2g is smaller than that of the rear J-sleeve 9b; because those
relations of the outer diameters may enhance the productivity of
the Rx unit 2 and the rear J-sleeve 9b. When the outer diameter of
the flange 2g is smaller than those of other two diameters, the
fillet welding between the members considerably becomes hard. The
rear J-sleeve 9b and/or the stem 2c would block the laser beam for
the welding.
[0033] Specifically, the flange 2g preferably has a thickness
greater than 0.3 mm. A flange with an ordinary thickness of about
0.2 mm would be easily deformed by the resistance welding between
the cap and the stem, which means that a distance between the
surface 2h of the flange 2g and the optically sensitive surface 2i
of the PD 2a also varies. Also, the flange 2g preferably has a
width at least 0.5 mm for securing the alignment tolerance for the
rear J-sleeve 9b and the fillet welding.
[0034] Next, details of the coupling unit 4 and the primary
assembly 5 will be described as referring back to FIGS. 2 and 3.
The coupling unit 4 includes a sleeve 4a, a stub 4b, a bush 4c, and
a sleeve cover 4d. The sleeve 4a receives an optical ferrule
secured in end of the single optical fiber. The stub 4b in a front
half thereof is held by a rear portion of the sleeve 4a. The bush
4c in a rear portion thereof supports the rear portion of the stub
4b, while, the front portion of the bush 4c is inserted between the
sleeve cover 4d and the rear portion of the sleeve 4a; that is, the
rear portion of the sleeve 4a is inserted between the front portion
of the bush 4c and the front portion of the stub 4b. The insertion
of the rear portion of the sleeve 4a, that of the front portion of
the bush 4c may be carried out by press-fitting.
[0035] The stub 4b secures the coupling fiber 4e in a center
thereof. The optical ferrule of the external fiber may be
physically in contact to a tip of the coupling fiber 4e, which
realizes the physical contact (PC) therebetween, and the external
fiber may optically couple with the coupling fiber 4e without
causing Fresnel interfaces. The Rx unit 2 and the Tx unit 3 may
optically couple with the rear end of the coupling fiber 4e. In
other words, the rear alignment unit 9, the WDM filter 8a, and the
front alignment unit 6 may optically couple the Rx unit 2 with the
rear end of the coupling fiber 4e. The arrangement between the Tx
unit 3 and the coupling unit 4 may also optically couple the Tx
unit 3 with the rear end of the coupling fiber 2e. Thus, the PD 2a
in the Rx unit 2 and the LD in the Tx unit 3 may optically couple
with the external fiber. The rear end surface of the stub 4b is
inclined to the optical axis of the coupling fiber 4e, which
effectively prevent the Tx signal output from the Tx unit 3 from
returning the Tx unit 3.
[0036] The coupling unit 4 is fixed to the primary assembly 5
through the front alignment unit 6. The front J-sleeve 6b receives
the front lens holder 6a in a bore 6d thereof. The front lens
holder 6a secures the front lens 6c within a bore thereof, and the
front lens 6c concentrates the Tx signal output from the Tx unit 3
and transmitting through the WDM filter 8a onto the end of the
coupling fiber 4e. The front J-sleeve 6b is fixed to the front lens
holder 6a by the piercing welding after adjusting an insertion
depth of the front lens holder 6a into the bore 6d of the front
J-sleeve 6b, which is the optical alignment along the optical axis.
In this alignment, the end of the coupling fiber 4e is not always
positioned just on a focal point of the front lens 6c. When the end
of the coupling fiber 4e locates on the focal point of the front
lens 6c, the Tx signal output from the Tx unit 3 may couple with
the coupling fiber at a maximum efficiency. Such a condition
sometimes causes an excess optical power in the external fiber.
Accordingly, a de-focus tuning, where the end of the coupling fiber
4e is set in a position offset from the focal point of the front
lens 6c by adjusting the insertion depiction of the front lens
holder 6a into the bore 6d of the front J-sleeve 6b, may adjust the
optical power within a specified range.
[0037] The optical alignment in a plane perpendicular to the
optical axis may be carried out by sliding the coupling unit 4 on a
surface 6e of the front J-sleeve 6b. After the optical alignment,
the fillet welding may fix the coupling unit 4 to the front
alignment unit 6.
[0038] The Tx unit 3 may be fixed to the primary assembly 5 by
procedures similar to those for the Rx unit 2. The Tx unit 3 is
fixed to the primary assembly 5 in a position opposite to the front
alignment unit 6. The optical axis of the Tx unit 3 becomes
substantially in parallel to the optical axis of the coupling unit
4. The Tx unit 3 provides a lens in an output port thereof that
collimates the Tx signal output from the Tx unit 3. The optical
module 1 of the present embodiment installs the optical coupling
system processing collimated beams because the WDM filter 8a
requires collimated beams to distinguish the beams depending on
respective wavelengths. When two optical beams entering the WDM
filter 8a have respective wavelength closely to each other, the
incident angles of the optical beams are necessary to be within
.+-.0.5.degree. to distinguish the optical beams effectively.
[0039] The optical module 1 of the present embodiment implements
the WDM filter 8a on the filter holder 8 that is inserted into the
housing 7 from a side thereof. Also, the optical module 1, in order
to precisely determine angles of the normal line of the WDM filter
8a with respect to the optical axes of the Rx unit 2 and the Tx
unit 3, respectively, provides slopes 7b in the housing 7 and
slopes 8b in the filter holder 8. Referring to FIGS. 2 and 3, the
housing 7 provides a bore (Tx bore) 7a whose axis substantially in
parallel to the optical axis of the coupling unit 4 and another
bore (Rx port) into which the filter holder 8 is inserted. Also,
the filter holder 8 provides a bore (Tx bore) 8e and another bore
(Rx bore) 8d, where the Tx bore 8e connects to the Tx bore 7a of
the housing 7, while, the Rx bore 8d connects to the Rx bore 7c of
the housing 7. Inserting the filter holder 8 into the Rx bore 7c of
the housing 7, and mating the slopes 8b of the filter holder 8 with
the slopes 7b of the housing without forming any gaps therebetween;
the filter holder 8 is automatically aligned with the housing 7.
Also, the Tx bore 8e and the Rx bore 8d expose on the mounting
surface 8c, that is, the axis of the Tx bore 8e intersects with the
axis of the Rx bore 8d at the surface of the WDM filter 8a mounted
on the mounting surface 8c. Moreover, the mounting surface 8a of
the filter holder 8, where the WDM filter 8a is mounted, is
mechanically aligned with the slopes 8b, the angle of the WDM
filter 8a with respect to the optical axis of the Rx unit 2 and
that of the Tx unit 3 may be automatically determined That is, the
normal line of the WDM filter 8a automatically makes an angle of
45.degree. with respect to the optical axis of the Rx unit 2 and to
the Tx unit 3.
[0040] Next, practical procedures of the optical alignment of the
optical module 1 will be described.
[0041] First step inserts the filter holder 8, which secures the
WDM filter 8a in the top thereof, into a side bore of the housing
7. Because the filter holder 8 provides the slopes 8b and the
housing 7 also provides the slopes 7b, both members, 7 and 8, may
be automatically aligned by setting the slopes 8b of the filter
holder 8 within the slopes 7b of the housing 7. The laser welding
may fix the filter holder 8 with the WDM filter 8 to the housing
7.
[0042] Second step fixes the Tx unit 3 to the housing 7.
Specifically, the Tx unit 3 is fixed to a surface, which is
opposite to the surface to which the front alignment unit 6 is
fixed, by the fillet welding. The process does not perform the
optical alignment between the Tx unit 3 and the housing 7; that is,
the Tx unit 3 is fixed to a designed position of the housing 7.
[0043] The third step fixes the coupling unit 4 to the housing 7
through the front alignment unit 6. Specifically, the procedure
prepares a dummy fiber that interlock with the front lens holder 6a
and has an end surface positioning substantially on the focal point
of the front lens 6c. Sliding the front lens holder 6a on the
surface of the housing 7 as sensing the Tx signal practically
output from the Tx unit 3, the process fixes the front lens holder
6a at a position at which the Tx signal sensed through the dummy
fiber becomes a maximum.
[0044] Then, removing the dummy fiber and covering the front lens
holder 6a by the front J-sleeve 6b, the coupling unit 4 is
temporally aligned at a position in the plane perpendicular to the
optical axis by sliding the coupling unit 4 on the surface 6e of
the front J-sleeve 6b where the maximum optical power of the Tx
signal detected through the coupling unit 4 becomes a maximum. The
insertion depth of the front lens holder 6a into the front J-sleeve
6b is adjusted at this point. Practically activating the LD in the
Tx unit 3, the insertion depth may be determined at a position
where the optical power sensed through the coupling fiber 4e
becomes in a preset range, and the front J-sleeve 6b is fixed to
the front lens holder 6a by the piercing welding. The optical
alignment between the front lens holder 6a and the front J-sleeve
6b is not always set in the position where the end of the coupling
fiber 4e is aligned with the focal point of the front lens 4c;
because, when the end of the coupling fiber 4e is in the focal
point of the front lens 6c, the optical power output from the
coupling fiber 4e sometimes exceeds the eye-safety range.
Accordingly, the end of the coupling fiber 4e is usually set in a
de-focused point of the front lens 6c. Finally, the alignment of
the coupling unit 4 in the plane perpendicular to the optical axis
is precisely performed by sliding the coupling unit 4 on the end
surface 6e of the front J-sleeve 6b. The coupling unit 4 is fixed
to the front J-sleeve 6b at thus determined position by the fillet
welding.
[0045] The fourth step aligns the Rx unit 2 to the housing 7,
exactly the filter holder 8m and fixes thereto. Specifically, the
process first fixes the rear lens holder 9a to the end surface of
the filter holder 8 without performing any alignment. That is, the
rear lens holder 9a is fixed in the designed position of the filter
holder 8 by the fillet welding. Then, the insertion depth of the
front lens holder 9a into the bore 9d of the rear J-sleeve 9b is
first adjusted. Interlocking the Rx unit 2 with the rear J-sleeve
9b, and providing a dummy Rx signal from the coupling unit 4, the
optical alignment of the Rx unit 2 with the rear J-sleeve 9b may be
carried out by practically detecting the Rx signal by the PD 2a in
the Rx unit 2. Because the WDM filter 8a is aligned in the angle
thereof, the dummy Rx beam enters the Rx unit 2 without performing
the optical alignment of the Rx unit 2 in the plane perpendicular
to the optical axis. Or, the dummy Rx signal enters the PD 2a in
the Rx unit 2 with optical power by which at least the optical
alignment along the optical axis enables. The insertion depth of
the rear lens holder 9a is set at the position where the optical
power sensed by the PD 2a becomes a maximum, and the rear J-sleeve
9b is fixed to the rear lens holder 9a by the piercing welding.
Subsequently, the optical alignment in the plane perpendicular to
the optical axis is performed. As described, the outer diameter of
the cap 2e of the Rx unit 2 is slightly smaller than the diameter
of the bore 9d of the rear J-sleeve 9b, which forms a gap
therebetween. The optical alignment is performed within this gap,
and the Rx unit 2 is fixed to the rear J-sleeve 9b at the position
where the optical power detected by the PD 2a becomes a maximum by
the fillet welding. Thus, the process to assembly the optical
module 1 is completed.
[0046] The optical alignment of the Rx unit 2 in the plane
perpendicular to the optical axis does not rotate the Rx unit 2,
because the Rx unit 2 provides lead terminals 2b that is to be
fixed to respective pads on the circuit board. When the Rx unit 2
rotates in the optical alignment thereof, the positional relations
between the lead terminals 2b and the pads are disordered. Also,
when an Rx unit provides, instead of the window 2f, a lens to
concentrate an Rx signal on the PD mounted on the stem, the optical
alignment in the plane perpendicular to the optical axis is
sometimes performed by rotating the stem 2c. However, the Rx unit 2
of the present embodiment, as described above, the rotation of the
stem 2c is prohibited. Accordingly, the optical alignment in the
plane perpendicular to the optical axis is done by forming a gap
between the cap 2e and the bore 9d of the rear J-sleeve 9b. In such
a case, the fillet welding for the Rx unit 2 to the rear J-sleeve
9b possibly inclines the Rx unit 2 with respect to the housing 7.
Because the fillet welding, or the welding, locally melts the
members to be welded, then solidifies the melted members to fix
them; the members to be welded, namely, the rear J-sleeve 9b and/or
the flange 2g of the cap 2e possibly deviate one aligned positional
relation during the melting. Accordingly, the Rx unit 2, which is
once aligned in the end 2h of the flange 2g thereof with respect to
the end surface 9e of the rear J-sleeve 9b, which possibly makes
the optical axis of the Rx unit 2 inclined with respect to the axis
of the rear J-sleeve 9b. Even in such a case, the Rx signal coming
from the housing 7 and entering the Rx unit 2 does not miss the
optically sensitive surface of the PD 2a.
[0047] While particular embodiments of the present invention have
been described herein for purposes of illustration, many
modifications and changes will become apparent to those skilled in
the art. Accordingly, the appended claims are intended to encompass
all such modifications and changes as fall within the true spirit
and scope of this invention.
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